Thermal shunt for a battery

ABSTRACT

A thermal shunt is provided for a battery contained in a thermally insulated container. The thermal shunt comprises an external heat sink, a heat conducting fluid, and a pump fluid which urges the heat conducting fluid into thermal contact with battery.

The present invention concerns a thermal shunt for a battery, inparticular, a battery which must be thermally insulated to retain heat,such as a battery made up of cells having a solid electrolyte andelectrodes of molten materials.

A typical example of such a cell is a sodium sulphur cell which willemploy liquid sodium as the anode and liquid sulphur as the cathode, thetwo being separated by a solid electrolyte of beta alumina which iselectronically insulating but conductive to cations of the alkali metal.

A battery will comprise several of the cells connected together within athermally-insulated container or battery box. Because theelectrochemical reaction will only proceed efficiently at elevatedtemperatures, the typical operating temperature is about 350° C.

During charging and discharging of the cells, heat is generated due tointernal resistances, for example, and builds up within the battery box.Although some of this internal heat energy is offset to some extent bythe slow natural cooling of the battery, this cooling is not sufficientto keep the temperature at the desired operating value, especially incases where the insulation of the battery box is particularly efficientor the duty particularly arduous.

Since increases in temperature are undesirable and if allowed to proceedtoo far will lead to overheating of the battery which could result indamage, ways have been considered of providing means whereby heat isallowed to be conducted out through the insulating battery container.

Accordingly, the present invention provides a thermal shunt for abattery contained in a thermally-insulating container comprising anexternal heat sink and means, connected between the heat sink and thebattery, which at a predetermined temperature are actuated to conductheat from the battery to the heat sink, thereby increasing the heat lossfrom the battery.

Preferably, the means connecting the heat sink to the battery is athermally conductive fluid which makes thermal contact with both thebattery and heat sink only when the predetermined temperature isreached.

Preferably, the thermal shunt further comprises a pump which at thepredetermined temperature urges the thermally conductive fluid to make athermal contact between one or more selected points on the batterysurface and heat sink.

Preferably, the pump supplies fluid to one or more containers connectedbetween the battery and the heat sink.

Preferably, the containers are bellows.

Preferably, the thermal shunt is arranged on the lower surface of thebattery.

In a second embodiment of the present invention the thermal shuntfurther comprises a pump which supplies pressurised gas or vapour to oneor more containers holding the thermally conductive fluid.

Preferably, the container or containers for the fluid is a concentricbellows arrangement, the gas or vapour being delivered to the bellowsarrangement to urge the fluid to make thermal contact between thebattery and the heat sink.

Preferably, the gas or vapour is delivered to the inner bellows and thefluid is urged between the inner and outer bellows to make thermalcontact between the battery and heat sink.

Preferably, the thermal shunt is arranged on the upper surface of thebattery.

In a third embodiment of the present invention the means connecting thebattery to the heat sink is one or more partially filled containers ofliquid located between the heat sink and battery, the liquid beingmaintained at a given pressure such that it will boil at thepredetermined temperature to release vapour which will condense in thevicinity of the heat sink to effect heat conduction from the battery tothe heat sink.

Preferably, the liquid is mercury pressurised to substantially 1.034×10⁵Nm² which will boil at substantially 350° C.

Preferably, the thermal shunt is arranged on the upper surface of thebattery.

Preferred embodiments of the present invention will now be described indetail, by way of example only, with reference to the accompanyingdrawings of which:

FIG. 1 is a schematic sectional view of a battery provided with athermal shunt according to a first embodiment of the present invention;

FIG. 2 is a view in direction II--I1 of the arrangement in FIG. 1;

FIG. 3 is an enlarged view of one of the bellows connections in FIG. 1;

FIG. 4 is a schematic sectional view of a battery provided with athermal shunt according to a second embodiment of the present invention;

FIG. 5 is a view in direction V--V of the arrangement in FIG. 4;

FIG. 6 is an enlarged view of one of the bellows connections in FIG. 4;

FIG. 7 is a schematic sectional view of a battery provided with athermal shunt according to a third preferred embodiment of the presentinvention;

FIG. 8 is a view taken in direction VIII--VIII in FIG. 7;

FIG. 9 is an enlarged view of one of the containers in FIG. 7.

The first preferred embodiment of the present invention is depicted inFIGS. 1 to 3. The thermal shunt, generally indicated by referencenumeral 1, is connected to a battery 2 in a thermally-insulatingcontainer or box 3. The thermal shunt 1 comprises an external heat sink4 and bellows 5 connected between the heat sink 4 through the container3 to the battery 2. The bellows 5 are supplied with a thermallyconductive liquid which is delivered from a reservoir 6 via a pump 7through a distribution manifold 8. The centre bellows 5 is supplied withthe liquid before the others which surround it. The complete arrangementis surrounded by a pannier 9. In FIG. 2 the distribution manifold 8 canbe clearly seen.

FIG. 3 is an enlarged view of one of the bellows 5 in FIG. 1. In thearrangement of FIGS. 1 to 3 the thermal shunt is located on the lowersurface of the battery 2, the liquid supply being such that liquid 10rises in the bellows 5 eventually making thermal contact between theheat sink 4 and battery 2. There is a collection point 14 for gastrapped in the bellows 5 before the liquid 10 is pumped into thearrangement. In this figure the inner 11 and outer 12 containers for thebattery 2 can be seen--the thermally-insulating container 3 is locatedbetween containers 11 and 12. The end cap 13 of the bellows 5 is boltedto the heat sink 4 by bolt 16 which then provides a good thermal contactbetween the heat sink 4 and liquid 10.

In use, the arrangement is provided with a switching mechanism (notshown) which is switched on when the battery 2 reaches a predeterminedtemperature of approximately 350° C. The reservoir will then releaseliquid which is pumped by pump 7 into the distribution manifold 8. Eachof the bellows 5 is then supplied with liquid 10 which fills the bellows5 and eventually makes thermal contact with the lower surface of thebattery via heater plate 15. There will then be thermal contact betweenthe battery 2 and heat sink 4 so that heat will be conducted through thebattery box 3 via the liquid 10, end cap 13 and bolt 16 to the heat sink4. When the temperature of the battery 2 falls sufficiently the liquidsupply will be cut off and the level of liquid 10 in bellows 5 will falluntil thermal contact is broken.

The second embodiment of the present invention is depicted in FIGS. 4 to6. The thermal shunt, generally indicated by reference numeral 21 isconnected to a battery 22 in a thermally-insulating container or box 23.The thermal shunt 21 comprises an external heat sink 24 and bellows 25connected between the heat sink 24 through the container 23 to thebattery 22. The bellows 25 comprise inner 25a and outer 25b bellows (seeFIG. 6) and contain a predetermined level of thermally conductive liquid20. A gas pump 27 delivers a gas via a distribution manifold 28 to eachof the bellows 25. FIG. 5 is a sectional view of the arrangement takenin direction V--V in FIG. 4 and it can be seen that the distributionmanifold 28 supplies nine bellows 25, the centre bellows being suppliedbefore the others which surround it. The complete arrangement issurrounded by a pannier 29 and rests on battery support cross members 26which may form the base of the pannier 29.

FIG. 6 is an enlarged view of one of the bellows 25 in FIG. 4. In thearrangement of FIGS. 4 to 6 the thermal shunt is located on the uppersurface of the battery 22. The bellows 25 each contain sufficientthermally-conductive liquid 20 such that when the gas is supplied to theinner bellows 25a the liquid 20 can rise in the volume between the inner25a and outer 25b bellows to make thermal contact between the battery 22and heat sink 24. There is a collection point 33 for gas trapped in thebellows before the gas is pumped into the arrangement. The inner andouter containers 31 and 32 for the battery 22 can be seen in FIG. 6 andnut 35 and O-ring 34 which serve to seal the air distribution manifold28 to the bellows 25.

In use, the arrangement is provided with a switching mechanism (notshown) which is switched on when the battery 22 reaches a predeterminedtemperature of approximately 350° C. The pump 27 will then be activatedand gas will be pumped via the distribution manifold 28 to each of thebellows 25. The gas supplied to the bellows 25 will force the liquid 20to rise and make a thermal contact between the battery 22 and heat sink24. Heat will then be conducted away from the battery 22 until thetemperature falls sufficiently to switch off the gas pump 27 which inturn will break the thermal contact between battery 22 and heat sink 24.

The third embodiment of the present invention is depicted in FIGS. 7 to9. The thermal shunt, generally indicated by reference numeral 41 isconnected to a battery 42 in a thermally-insulating container or box 43.The thermal shunt 41 comprises an external heat sink 44 and severalpressurised mercury containers 45 connected between the heat sink 44through the container 43 to the battery 42. The pressurised mercurycontainers 45 typically contain mercury 54 which is pressurised to1.034×10⁵ Nm². Since the boiling point of mercury is a function ofpressure, the pressure in volume 55 above the mercury 54 can be adjustedsuch that the mercury will boil at approximately 350° C. which is theupper temperature of operation for the battery. At 1.034×10⁵ Nm² themercury boils at 350° C. and vapour will rise in the container 53 andcondense on the cooler upper surface which is in contact with the heatsink 44 via outer container 52. The container 53 need only haveconductive upper and lower surfaces for heat conduction to occur fromthe battery 42 to the heat sink 44. The walls of the container 53 could,therefore, be made from a thermally insulating material such as aceramic, for example.

In use, the arrangement is located on the upper surface of battery 42such that the mercury 54 is in thermal contact with the battery viainner container 51 and the mercury container 53. When the temperature ofthe battery rises to 350° C. the mercury 54 will boil, release vapourwhich then gives up its latent heat when it condenses on the coolerupper surface of the container 53. Heat conduction will continue in thisway until the temperature of the battery falls sufficiently and themercury is below its boiling point. Below the boiling point of themercury there is negligible heat conduction. The complete arrangement issurrounded by a pannier 49 and rests on battery support cross members 46which may form the base of the pannier 49.

We claim:
 1. A battery arrangement comprising:a thermally insulatingcontainer; a battery having a battery surface with one or more selectedpoints, the battery being contained within the thermally insulatedcontainer; and a thermal shunt, the thermal shunt includingan externalheat sink, one or more containers for holding a thermally conductivefluid, the one or more containers connecting respective ones of the oneor more selected points on the battery surface and the external heatsink, a pump arranged to supply a pump fluid to the one or morecontainers to urge the thermally conductive fluid to make thermalcontact between the one or more selected points on the battery surfaceand the external heat sink, and temperature responsive means foractuating the pump.
 2. A battery arrangement as claimed in claim 1wherein the pump fluid includes the thermally conductive fluid.
 3. Abattery arrangement as claimed in claim 2 wherein the one or morecontainers are bellows.
 4. A battery arrangement as claimed in any oneof claims 2, 3, and 1 wherein the battery surface is a lower surface ofthe battery.
 5. A battery arrangement as claimed in claim 1 wherein thepump fluid is any one of a pressurized gas and vapor.
 6. A batteryarrangement as claimed in claim 5 in which the one or more containersare provided as concentric bellows arrangements having inner and outerbellows, the gas or vapor being delivered to the bellows arrangements tourge the thermally conductive fluid to make thermal contact between theone or more selected points on the battery surface and the external heatsink.
 7. A battery arrangement as claimed in claim 6 wherein the gas orvapor is delivered to the inner bellows and the thermally conductivefluid is urged between the inner and outer bellows to make thermalcontact between the one or more selected points on the battery surfaceand the external heat sink.
 8. A battery arrangement as claimed in anyone of claims 5-7 wherein the battery surface is an upper surface of thebattery.